1 University of Canberra Advanced Communications Topics Television Broadcasting into the Digital Era by: Neil Pickford Lecture 1 Television History Analog TV Fundamentals

2 Overview of Topics 1 - Basic Concepts of Television Systems 2 - Digital Video Sampling & Standards 3 - Digital Audio/Video Stream Compression 4 - Digital Modulation Systems 5 - Transmission System Error Protection 6 - Digital System Parameters, Planning and SI

3 Digital Media n First media systems were analog n Most media are converting to digital u Computer storage u Music (LP-CD) u Telecommunications u Multimedia u Internet Networking (TCPIP) u Radio (DAB) u Television (DTTB)

4 What is Television n Images - Black and White Shades of Grey n Colour - Hue & Saturation n Sound - Audio Information n Data - Teletext & Other Data n Synchronisation - Specifies the Timing n Transport System - Gets the Above to your TV

5 History - Ferdinand Braun - CRT n 1890 Ferdinand Braun developed the Cathode Ray Tube. n 1897 developed the Cathode Ray Oscillograph, the precursor to the radar screen and the television tube n 1907 First use of cathode ray tube to produce the rudiments of television images. n He shared the Nobel Prize for physics in 1909 with Guglielmo Marconi for his contributions to the development of wireless telegraphy.

6 John Logie Baird - Basic TV n Oct 1923 John Logie Baird was the first person anywhere in the world to demonstrate true television in the form of recognisable images, instantaneous movement and correct gradations in light and shade. Scanning was done mechanically with a Nipkow disc. The first 30 line picture transmitted was a Maltese cross. n 1927 he also demonstrated video recording n 1928 transatlantic television n 1937 the broadcast of high definition colour pictures n 1941 stereoscopic television in colour n 1944 the multi-gun colour television tube, the forerunner of the type used in most homes today.

7 Early Mechanical Approach to TV Mechanical Nipkow discs were used to scan the image and reconstitute the image at the receiver. PE cells were used to capture the image. The problem was synchronising the disks.

8 30 Line Mechanical TV

9 Electronic Television - Farnsworth n In 1922 at Age 14 Philo Farnsworth had the idea of how to make Electronic Television possible. n Sept. 7, 1927, Farnsworth painted a square of glass black and scratched a straight line on the centre. The slide was dropped between the Image Dissector (the camera tube that Farnsworth had invented earlier that year) and a hot, bright, carbon arc lamp. On the receiver they saw the straight-line image and then, as the slide was turned 90 degrees, they saw it move. This was the first all-electronic television picture ever transmitted.

10 Vladimir Zworykin - Iconoscope n In 1923 Vladimir Zworykin of RCA made a patent application for a camera device, and by 1933 had developed a camera tube he called an Iconoscope. Although Zworykin submitted his patent application first after many years of legal battle Farnsworth was acknowledged as the inventor of electronic television. n By the end of 1923 he had also produced a picture display tube, the "Kinescope"

11 Significant Television Inventions n These inventions were the underlying basis of the development of Television as we know it today

12 Aspect ratio n First TV displays were Round n Rectangular Rasters easier to Generate n Television Developed a 4:3 Aspect Ratio 4:3 (12:9) 16:9 n Cinematic formats are much wider n World now moving to 16:9 Aspect Ratio

13 Film n Has been the highest Resolution storage format. n Various frame sizes used. 16mm, 35mm & 70mm n Difficult to produce, store, handle and display. n Easily degraded due to contamination and scratches. n Generally recorded at 24 fps. n Generally displayed at 72 fps (each frame 3x) to reduce flicker n Use a device called a Telecine to convert to television formats

14 The Video Signal n First Television Pictures were Black & White Referred to as Luminance n Video refers to the linear base-band signal that contains the image information Front Back Porch Grey Background Sync Pulse White Stripe Black Stripe 0 mV 700 mV -300 mV

15 Video Timing n SDTV 1 Line = 64 us Active Picture 52 us Sync 4.7 us Line Blanking 12 us u 64 us for each line ( kHz) u 52 us Active Picture Area u 12 us Blanking and Synchronisation n Two level sync pulse 300 mV below blanking

16 Frame Rate n A Frame represents a complete TV picture n Our analog TV Frame consists of 625 lines. n A Frame is usually comprised of 2 Fields each containing 1/2 the picture information n Our system has a Frame rate of 25 Hz n The Field rate is 50 Hz n Pictures displayed at 25 Hz exhibit obvious flicker n Interleaving the Fields reduces flicker.

17 Flickerand Judder n Flicker and Judder are terms used to describe visual interruptions between successive fields of a displayed image. It affects both Film & TV. n If the update rate is too low, persistence of vision is unable to give illusion of continuous motion. n Flicker is caused by: u Slow update of motion Information u Refresh rate of the Display device u Phosphor persistence Vs Motion Blur n Judder usually results from Aliasing between Sampling rates, Display rates and Scene motion

18 Interlace n To reduce the perceived screen flicker (25 Hz) on a television, a technique called 'interlacing' is employed. n Interlacing divides each video frame into two fields; the first field consists of the odd scan lines of the image, and the second field of each frame consists even scan lines. n Interlace was also used to decrease the requirement for video bandwidth. It is a form of Compression

19 Interlaced Vs Progressive Scan n Interlaced pictures. - 1/2 the lines presented each scan 1,3,5,7,9,11, ,625 field 1 2,4,6,8,10,12, ,624 field 2 n Because the fields are recorded at separate times this leads to picture twitter & judder n Progressive pictures - all the lines sent in the one scan. 1,2,3,4,5,6,7, ,624,625 picture n No twitter or judder. n But twice the information rate.

20 Progressive Scan n Simplifies the interpolation and filtering of images n Allows MPEG-2 compression to work more efficiently by processing complete pictures n Direct processing of progressively-scanned sources n 24 frame/second progressive film mode can be provided. n Assists video conversions with different: u numbers of scan lines u numbers of samples per line u temporal sampling (i.e., picture rate) Progressive Doubles Raw Data Requirement

21ResolutionResolution n The number of picture elements resolved on the display n Resolution in TV is limited by: u Capture device u Sampling Rate u Transmission System / Bandwidth u Display Device F Dot Pitch, Phosphor F Focus & Convergence u Viewing distance / Display size u Human Eye n Typical SDTV systems attempt to transfer 720 pixels per line

22 Colour Equations for PAL n For B&W only had to transmit Luminance (Y) n A Colour Image has Red, Green & Blue Components which need to be transmitted. n We already have the Y signal. n To remain compatible with Monochrome sets use Y, U & V to represent the Full Colour Picture Y = R G B U = (B - Y) V = (R - Y) Colour Difference Signals

23 A Compatible Colour System Y V U RGBRGBRGBRGB Y

24 Colour Sub Carrier n Colour Sub- Carrier is added at MHz n Frequency selected to interleave colour information spectra with Luma spectrum n More efficient use of spectrum.

25 Adding Colour to B&W Video First TV signals were only Luminance In 1975 we added PAL Colour System A Colour Reference Burst on Back Porch And IQ modulated Colour Information

26 Amplitude Modulation

27 Television Modulation - AM n TV uses Negative AM Modulation 0% 0% 100% 100%

28 TV Modulation - AM Min 20% n Peak White 20% Black 76% Syncs 100% 20% 20% 0% 0% 76% 76%100%100%

29 TV Modulation - PAL AM n n Headroom prevents Colour Over/Under Modulating 20% 20% 0% 0% 76% 76%100%100%

30 Frequency Modulation

31 Intercarrier Sound n A FM subcarrier is added to the AM picture to carry the Audio information n FM Deviation 50 kHz used with 50 us Emphasis n PAL-B uses 5.5 MHz Sound subcarrier (L+R) u -10 dB wrt Vision for mono single carrier mode u -13 dB wrt Vision for Stereo & Dual mode n 2nd Sound subcarrier for Stereo (R) u MHz ( kHz above main sound) u -20 dB wrt Vision carrier u 54.7 kHz Subcarrier Pilot tone added to indicate: Stereo (117.5 Hz) or Dual mode (274.1 Hz)

32 FM Sound Emphasis dB Frequency (Hz)

33 TV Modulation - Sound n n FM Sound Subcarriers Superimpose over the AM 20% 20% 0% 0% 76% 76%100%100%

34 NTSC n National Television Systems Committee (NTSC) n First world wide Colour system Adopted (1966) n Generally used in 60 Hz countries n Predominantly 525 line TV systems n AM modulation of Luma & Syncs (4.2 MHz) n U & V Chroma AM Quadrature Modulated (IQ) n Chroma Subcarrier MHz n FM or Digital subcarrier modulation of Sound

35 SECAM n Sequentiel Couleur Avec Memoire (SECAM) n Developed by France before PAL n 625 Line 50 Hz Colour system n Uses AM modulation for Luminance & Sync n Line sequentially sends U & V Chroma components on alternate lines n Receiver requires a 1H chroma delay line n Uses FM for Colour subcarrier MHz n Uses FM for sound subcarrier

36 PAL n Phase Alternation Line-rate (PAL) Colour System n Developed in Europe after NTSC & SECAM n Generally associated with 50 Hz Countries n Predominantly 625 Line system n AM modulation of Luma & Syncs (5 MHz) n U & V Chroma AM Quadrature Modulated with V (R-Y) component inverted on alternate lines n Chroma Subcarrier MHz n FM or Digital subcarrier modulation of Sound

37 Vestigial Side Band - VSB n AM Modulation gives a Double Side Band signal u Each sideband contains identical information u 5 MHz of information means required BW > 10 MHz u Only one sideband is required for demodulation n To conserve spectrum Analog TV uses VSB u Only 1.25 MHz of the lower sideband is retained u VSB truncates the high frequency part of the lower sideband. n To implement Analog TV with no lower sideband would have been very expensive because of the filtering required.

38 PAL-B Spectrum Sound -13 dB Sound -20 dB 0 dB Vision Carrier Chroma Relative Frequency (MHz) Truncated Lower Sideband

39 Frequencies Used n Australia uses 7 MHz Channels n VHF Band ICh MHz n VHF Band IIICh MHz n UHF Band IV Ch MHz n UHF Band VCh MHz

40 World TV Standards Australia is PAL NTSC PAL SECAM PAL/SECAM Unknown

41 Transmission Bandwidth - VHF Australia is one of a few countries with 7 MHz VHF TV 6 MHz 7 MHz 8 MHz Not in Use

42 Transmission Bandwidth - UHF 6 MHz 7 MHz 8 MHz Not in Use Australia is Alone using 7 MHz on UHF

43 U & V Components Y = R G B B-Y = R G B R-Y = 0.701R G B U’ = B-Y V’ = R-Y

44 Y, B-Y & R-Y Values B-Y = R G B B-Y Range is too large

45 Y, B-Y & R-Y Values R-Y = 0.701R G B R-Y Range is too large

46 Y, U & V Values U = (B-Y) V = (R-Y)

47 Component Video n Video distributed as separate Y U V Components n Y signal is 700 mV for Video Black-White n Y Signal carries Sync at -300 mV n U & V signals are 700 mV pk-pk. 350 mV at mV 0 mV 700 mV -300 mV YVU

48 Coax n Video Signals are transmitted on Coaxial Cable n 75 Ohm Coax - RG-59 or RG-178 n Video is usually 1 Volt Peak to Peak n Terminated with 75 Ohms at end of run n High impedance loop through taps are used n To split video must us a Distribution Amplifier n For Component signals all coax’s must be the same length otherwise mistiming of the video components will occur

49 Standard Definition Television SDTV n The current television display system n 4:3 aspect ratio picture, interlace scan n Australia/Europe u 625 lines pixels x 576 lines displayed u 50 frames/sec 25 pictures/sec u pixels total n USA/Japan u 525 lines pixels x 480 lines displayed u 60 frames/sec 30 pictures/sec u pixels total

50 Enhanced Definition Television EDTV n Intermediate step to HDTV n Doubled scan rate - reduce flicker n Double lines on picture - calculated n Image processing - ghost cancelling n Wider aspect ratio - 16:9 n Multi-channel sound

51 High Definition Television - HDTV n Not exactly defined - number of systems n System with a higher picture resolution n Greater than 1000 lines resolution n Picture with less artefacts or distortions n Bigger picture to give a viewing experience n Wider aspect ratio to use peripheral vision n Progressive instead of interlaced pictures